If two persons with 'AB' blood group marry and have sufficiently large number of children, these children could be classified as 'A' blood group: 'AB' blood group : 'B' blood group in 1 : 2 : 1 ratio. Modern technique of protein electrophoresis reveals presence of both 'A' and 'B' type proteins in 'AB' blood group individuals. This in an example of
In the case of co-dominance the generation resembles both parents. A good example is different types of red blood cells that determine ABO blood grouping in human beings. ABO blood groups are controlled by the gene (I). This gene (I)has three alleles , and i. The alleles and produce a slightly different form of the sugar while allele i does not produce any sugar.
When and are present together they both express their own types of sugars: this is because of co-dominance. Hence red blood cells have both A and B types of sugars.